Since cemented carbide is a relatively expensive material and since cutting tool inserts, when worn-down, must be scrapped and exchanged at relatively short intervals, it is generally desirable to make the inserts for cutting tools as small as possible. Especially during intense processing of the workpieces involved, large amounts of heat are generated in the cutting edge portion of the insert. That heat is conducted through the remainder of the insert. Since the inserts are small and, in conventional cut-off tools, are applied directly against the bottom wall of a recess in a holder plate, only a minor portion of the heat will be emitted into the ambient atmosphere before the heat reaches, in particular, the underlying bottom wall of the recess in the holder plate. This means that the temperature in the portion of the holder plate adjacent the bottom wall of the recess will rise to such a level that the steel material of this plate portion is liable to undergo considerable plastic deformation. This, in turn, may result in the cutting edge of the insert being moved out of its initial or reference position, which is accurately fixed in relation to the plate. This may entail considerable practical inconveniences, not only in the form of dramatically deteriorated measurement accuracy in the processed workpiece, but also, for example, in that the cutting edge, in the final phase of a cut-off operation, will not hit the center of the rotating workpiece. In serious cases, the plastic deformation and the consequential displacement of the insert may give rise to tool breakage as well.
The measure of providing a simple spacer plate between a cemented carbide insert and an insert holder in the form of a tool shank is previously known in connection with conventional turning tool holders. Further, from EP 0 000 426 and DE 31 19 834, it is previously known in connection with cut-off tools to arrange the insert in a special, detachable, substantially U-shaped insert which, in turn, is applied in the recess of the insert-holder plate. In these cases, the U-shaped insert must be made of a relatively elastic material, more specifically steel, which does not have particularly good heat-resisting properties, at least when compared to cemented carbide.
Moreover, U.S. Pat. No. 3,543,363 discloses a cut-off tool in which a special spacer element or anvil seat comprising an insert-receiving seat of V-shaped cross-section is disposed between the insert and the bottom wall of the recess in the holder plate. In this case, the anvil seat is permanently connected to the holder plate, more specifically by gluing or brazing the underside of the anvil seat to the bottom wall of the recess. Also, the anvil seat does not have the explicit function of making the removal of heat from the insert more effective (the U.S. publication is completely silent on the material of which the anvil seat is to be made). This means that simple and quick dismounting and remounting of the anvil seat is not possible. Moreover, the simple glue or solder layer between the anvil seat and the bottom wall of the recess provides no reliable retention of the anvil seat and the insert placed thereon, especially not when the insert is subjected to lateral stresses.